1. Field of the Invention
This invention relates generally to the sinking or installation of tubular well casings, and pertains more particularly to a well point and method of using same.
2. Description of the Prior Art
Well points, of course, are old and well known. Those with which I am familiar include a steel head with a conical or tapered tip at the bottom and a cylindrical screen thereabove. The upper end of the screen is threadedly attached to the first pipe section of the ultimate casing and the upper end of the first pipe section has a threaded drive cap temporarily screwed thereon. By means of a drive hammer the drive cap is repeatedly struck so as to drive the first pipe section and the well point attached to its lower end downwardly into the ground. When the next pipe section is to be added, the drive cap is removed and the next pipe section threadedly coupled to the first pipe section. The next or second pipe section is then driven downwardly and the action continued to form a well casing on the order of thirty feet or so under normal soil conditions, the length depending upon the depth of the water table to be reached. While the individual pipe sections can vary in length, they are customarily on the order of five feet in length.
Consequently, it can be appreciated that a sizable number of pipe sections must be coupled together to form the well casing and that it can become quite long. Because the column of pipe sections constituting the well casing is struck at its upper end, which upper end becomes increasingly more remote from the drill point at the bottom of the casing as more and more pipe sections are added, it follows that as the casing gets longer and longer, the casing progressively absorbs more and more of the blow due to its greater inertia plus the fact that the column compresses from the impact. Thus, the resultant force applied to the well point, which is at the lower end of the casing receives a smaller and smaller proportion of the hammer blow being applied at the casing's upper end. This can seriously limit the depth to which the casing or column can be driven. Also, the rather lengthy column of pipe sections can buckle or bow, the buckling or bowing becoming more pronounced when the soil formation is compacted, nonporous or rocky. A specific situation that frequently arises is that the well point may pass through, said, twenty feet of soft soil, then encountering a hard soil condition which must be penetrated by first transmitting the hammer blows through the rather massive twenty foot string of pipe sections before they reach the well point. Furthermore, inasmuch as the column is struck at its upper end, the well point is apt to "wander", the degree of wandering becoming greater and greater as the column lengthens; if the soil is hard and rocky, the well point is even more vulnerable to being deflected as it advances downwardly.